Refactor zen-browser-ui.css: Remove unnecessary background styling

src/browser/themes/linux/browser-css.patch

@@ -0,0 +1,22 @@
+diff --git a/browser/themes/linux/browser.css b/browser/themes/linux/browser.css
+index 963a33af85521914ba0dad973ef94e6a8c2afdd0..f31bd5261631cb9e00ee6b723d6f9a85f0ae3119 100644
+--- a/browser/themes/linux/browser.css
++++ b/browser/themes/linux/browser.css
+@@ -72,7 +72,7 @@
+     -moz-default-appearance: -moz-window-decorations;
+     appearance: auto;
+ 
+-    #navigator-toolbox,
++    #zen-main-app-wrapper,
+     dialog::backdrop {
+       border-top-left-radius: env(-moz-gtk-csd-titlebar-radius);
+       border-top-right-radius: env(-moz-gtk-csd-titlebar-radius);
+@@ -80,7 +80,7 @@
+ 
+     /* stylelint-disable-next-line media-query-no-invalid */
+     @media (-moz-bool-pref: "widget.gtk.rounded-bottom-corners.enabled") {
+-      #navigator-toolbox {
++      #zen-main-app-wrapper {
+         /* The body clip below covers this. */
+         border-radius: 0;
+       }